Digestive Development 2
Terms in this set (54)
How does the midgut communicate with the yolk sac?
By way of the vitelline duct
Where does the midgut begin?
Immediately distal to the entrance of the bile duct into the duodenum
Where does the midgut terminate?
At the junction of the proximal 2/3 of the transverse colon with the distal 1/3
What supplies blood to the entire midgut?
THE SUPERIOR MESENTERIC ARTERY*
Rapid elongation of the midgut results in the formation of what structure?
The primary intestinal loop
The loop remains in open communication with what structure?
With the yolk sac
What connects the intestinal loop with the yolk sac?
The vitelline duct
What does the cephalic limb of the intestinal loop develop into?
The distal part of the duodenum, the jejunum, and part of the ileum
What does the caudal limb of the intestinal loop develop into?
The lower part of the ileum, the cecum, the appendix, the ascending colon, and the proximal 2/3 of the transverse colon
What happens to the intestinal loop as a result of the rapid growth and expansion of the liver?
The abdominal cavity temporarily becomes too small to hold all the intestinal loops
Where does the intestinal loops go when the abdominal cavity becomes to small?
The loops enter the extra embryonic cavity in the umbilical cord
(the physiologic herniation)
What does the primary intestinal loop rotate around as it grows in length?
It rotates around the axis formed by the superior mesenteric artery
How does the primary intestinal loop rotate?
It rotates counterclockwise, approximately 270 degrees
- during herniation = 90 degrees
- during return of intestinal loops to abdominal cavity = 180 degrees
What is the first part of the intestinal loop to reenter the abdominal cavity?
What is the last part of the intestinal loop to reenter the abdominal cavity?
The cecal bud
Where does the cecal bud appear?
As a conical dilation of the caudal limb of the primary intestinal loop
During its migration, what forms at the distal end of the cecal bud?
A narrow diverticulum, the appendix
Where is the appendix frequently located?
Retrocecal or retrocolic
What does the hind gut give rise to?
The distal 1/3 of the transverse colon, sigmoid colon, rectum, and the upper part of the anal canal
What does the endoderm of the hind gut form?
The internal lining of the bladder and the urethra
What forms the primitive anorectal canal?
The terminal part of the hind gut entering the posterior portion of the cloaca
What forms the primitive urogenital sinus?
The allantois entering the anterior portion of the cloaca
What is the cloaca?
An endoderm lined cavity that is covered at the ventral boundary by ectoderm (the cloacal membrane)
From where is the urorectal septum derived?
From mesoderm surrounding the allantois and covering the yolk sac
What separates the allantois from the hind gut?
The urorectal septum
With growth and folding, does the urorectal septum ever make contact with the cloacal membrane?
What is formed when the cloacal membrane ruptures?
The anal opening for the hind gut
From where is the caudal portion of the anal canal derived?
From where is the cranial end of the anal canal derived?
What supplies blood to the ectodermal portion of the anal canal?
The inferior rectal arteries, a branches of internal pudendal artery
What supplies blood to the cranial part of the anal canal?
The superior rectal arteries, branches from the inferior mesenteric artery
What marks the junction between the ectoderm and endoderm in the anal canal?
The pectinate line
How does the epithelium change at the pectinate line?
From simple columnar epithelium to stratified squamous epithelium
What is Gastroschisis?
The herniation of the abdominal viscera through the body wall directly into the amniotic cavity
Where does gastroschisis occur?
Lateral to the umbilicus, usually on the right side
Does anything cover the herniating viscera in gastroschisis?
How can gastroschisis be detected before birth?
Elevated levels of alpha-fetoprotein are found in the amniotic fluid and can be detected prenatally
What may account for the increasing frequency of gastroschisis in females?
The increase may be related to cocaine use*
Is gastroschisis associated with chromosomal abnormalities or other severe defects?
What is Omphalocele?
The herniation of the abdominal viscera through an enlarged umbilical ring
Does anything cover the herniating viscera in omphalocele?
YES, the viscera are covered by amnion
What is the origin of the defect in omphalocele?
A failure of the bowel to return to the body cavity from its physiological herniation during the 6th week to the 10th week
What is omphalocele associated with?
- High mortality rate
- Severe malformations
- Cardiac anomalies
- Neural tube defects
Approximately 15% of live born infants with omphalocele have...
... chromosomal abnormalities*
What is Meckel's Diverticulum?
A small part of the vitelline duct that persists, forming an out pocketing called Meckel's diverticulum
What happens if a Meckel's diverticulum contains heterotopic pancreatic tissue or gastric mucosa?
It could cause ulceration, bleeding, or even perforation
What is an atresia?
A congenital absence of an opening or lumen
What is stenosis?
A narrowing of a canal or orifice
Where doe most atresias and stenoses occur along the intestine?
In the duodenum
What probably causes atresias in the upper duodenum?
Probably due to a lack of recanalization
What probably causes atesias from the distal duodenum caudally?
Most likely caused by vascular accidents
What may cause rectourethral and rectovaginal fistulas?
May be caused by abnormalities in formation of the cloaca and or the urorectal septum
What probably causes rectoanal atresias?
What occurs when the anal membrane fails to breakdown?
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